public class Test {
    public static void main(String[] args) {
        MyStack myStack=new MyStack();
        myStack.push(10);
        myStack.push(20);
        System.out.println(myStack.pop());
        System.out.println(myStack.peek());
        System.out.println(myStack.size());
        System.out.println(myStack.pop());
    }
}
